Plug-in hybrid vehicles or the like, in which a secondary battery which can be charged by connecting to a household electric wall socket is mounted, have been developed in recent years. For charging the secondary battery, charge control is performed such that a SOC (State of Charge) indicating the charged state of the secondary battery falls within a predetermined range. Here, while the SOC of a secondary battery can be estimated from an OCV (Open Circuit Voltage) of the secondary battery, as it is not possible to measure the OCV during charging of the secondary battery, the SOC of the secondary battery is estimated from a CCV (Closed Circuit Voltage) of the secondary battery. In this case, a relationship of CCV≈OCV+IR (wherein I represents electric current flowing in the secondary battery, and R is internal resistance of the secondary battery) is satisfied.
As technology related to the present invention, Patent Document 1, for example, discloses a charge control circuit for controlling the charging of a secondary battery. The charge control circuit has a structure including a voltage detection section which detects a terminal voltage of the secondary battery, an inclination acquisition section which interrupts charging during the charging of the secondary battery and performs inclination information acquisition processing for acquiring voltage inclination information indicating an amount of decrease of the terminal voltage per predetermined time from the terminal voltage detected by the voltage detection section during the interruption of the charging, and a charging termination determination section which executes determination processing for determining whether or not the charging of the secondary battery should be terminated based on the voltage inclination information acquired from the inclination acquisition section.